1. Field of the Invention
This invention relates to a process for the production of compacted granules, to the granules obtained by this process and to storable and free-flowing detergent concentrates containing the granules.
In the field of solid, free-flowing household and institutional detergents and particularly in the field of powder-form laundry detergents, there is a trend towards the manufacture of products having increased apparent densities. Recent commercial products of this type have apparent densities of the order of 700 g/l. This increase in apparent density is consistent with the need for less packaging dictated by environmental requirements. Efforts to market detergents in the form of relatively highly concentrated mixtures of ingredients are being made with the same object in mind. At first, reducing the amount of diluents in the concentrates as an unnecessary salt component appeared to be a solution to the problem. However, the problem at hand is not easy to solve in this way. Prerequisites for such formulation changes are understandably that, on the one hand, the detergent performance required by the consumer remains at least comparable with that of commercially available products and, on the other hand, the stability of pourable, free-flowing products should also be guaranteed. As documented by the extensive prior art on the subject, satisfying this requirement profile poses considerable technological problems.
2. Discussion of Related Act
Thus, German patent application 20 50 560 describes a process for the production of particulate ("noodle-shaped") detergents having apparent densities of 500 to 900 g/l, in which a premix of specific composition is compacted "under pressure"and subsequently converted into strand form. Unfortunately, there are no references to the intensity of the pressure to be applied. To prevent the strands from sticking together, they have to be cooled by means of an air stream before they are size-reduced to pieces of certain length. The apparent density is inversely proportional to the length of the pieces.
German patent application 21 62 353 describes a process for the production of enzyme granules and enzyme-containing detergent granules having an apparent density of 300 to 1,000 g/l. In this process, a mechanically precompounded paste is extruded under a pressure of about 7 to 35 bar to form a long strand. To prevent the strands from sticking together to form relatively large aggregates on leaving the extruder, they have to be "deplasticized". This is done either by cooling or by evaporation of the moisture, the solvent or the plasticizer (surface hardening). Only then can the strands be broken up into relatively small pieces of the required length.
According to the teaching of German patent application 22 24 300, granulated detergents having apparent densities of 300 to 800 g/l are obtained by extrusion and subsequent rounding of the spaghetti-like extrudates (Marumerizer). In this process, all the constituents are carefully mixed before extrusion in the quantities in which they are present in the end product. It is important to ensure that the constituents are selected and combined in such a way that they form a viscous or plastic paste before extrusion. Accordingly, variations to the detergent formulations are possible to only a limited extent.
European patent application 328 880 describes a process for the production of detergent extrudates having apparent densities of 700 to 800 g/l, in which a powder-form premix is initially extruded to spaghetti-like strands under reduced pressures of 0.1 to 0.5 bar. The strands are then broken up into pieces which, in turn, are extruded into special predetermined shapes. To ensure that the individual end products have the same weight, size reduction of the spaghetti-like strand into pieces is monitored by weighing.
European patent application 351 937 on the other hand describes a process for the production of detergent gran-ules having apparent densities of at least 650 g/l which, again, is dependent on the particular formulation. Thus, detergents containing 12 to 70% by weight surfactants must contain at least 15% by weight water-soluble, crystalline inorganic salts. The ratio of crystalline salt to surfactant must not fall below a value of 0.4. The detergents are dry-mixed in known mixers and granulated.
By contrast, European patent application 352 135 describes a process for the production of granular detergents having apparent densities of 650 g/l, in which a solid alkaline material is introduced into a mixer or granulator incorporating a cutting unit and liquid anionic surfactant in the acid form is added so slowly at temperatures not exceeding 55.degree. C. that the mixture remains solid throughout the entire neutralization process. The alkaline material has to be used in excess. Only on completion of neutralization can a liquid binder, for example water, liquid nonionic surfactant or an aqueous polycarboxylate solution, be added to the mixture. Granulation takes place in known mixers and granulators.
Finally, US-PS 3,188,291 describes a process for the production of granular soap carriers and detergents having low apparent densities in the range from about 16 to 480 g/l. In this process, the paste is extruded under pressures of from about 82 to 165 bar. Under higher pressures, the paste was too viscous and could no longer be extruded. By contrast, under pressures below 82 bar, the apparent density was too high. Accordingly, the teaching of this patent specification is that low apparent densities are obtained where relatively high pressures are applied during the extrusion process, the apparent density increasing with decreasing pressure.